• Journal of the Korea Concrete Institute
• /
• v.24 no.6
• /
• pp.633-641
• /
• 2012

In this study, the effects of the inelastic shear behavior of beam-column joint on the response of RC OMRF are evaluated in the inelastic time history analysis. For an example, a 5-story structure for site class SB and seismic design category C was designed in accordance with KBC2009. Bending moment-curvature relationship for beam and column was evaluated using fiber model and bending moment-rotation relationship for beam-column joint was calculated using simple and unified joint shear behavior model and moment equilibrium relationship. The hysteretic behavior was simulated using three-parameter model suggested in IDARC program. The inelastic time history analysis with PGA for return period of 2400 years showed that the model with inelastic beam-column joint yielded smaller maximum base shear force but nearly equivalent maximum roof displacement and maximum story drift as those obtained from analysis using rigid joint. The maximum story drift satisfied the criteria of KBC2009. Therefore, the inelastic shear behavior of beam-column joint could be neglected in the structural design.

• Journal of the Korea Concrete Institute
• /
• v.18 no.2 s.92
• /
• pp.257-266
• /
• 2006

Flat-plate building systems are utilized extensively for construction of apartments, hotels and office buildings because of short construction period, low floor-to-floor height and flexibility in plan design. Recently, to increase lateral seismic resistance of flat-plate building systems, wall-columns are used frequently. Therefore, to estimate strength of flat-plate column connection accurately, the effect of column section shape on the behavior of flat-plate column connection should be considered properly, In the present study, a numerical analysis was performed for interior connections of continuous flat-plate to analyze the effect of column section shape. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. Therefore, these effects should be considered properly to estimate the strength of flat-plate connection accurately.

• Economic and Environmental Geology
• /
• v.53 no.5
• /
• pp.585-596
• /
• 2020

The 2017 Pohang Earthquakes occurred near a drill site in the Pohang Enhanced Geothermal System. Water injected for well stimulation was believed to have reactivated the buried near-critically stressed Miocene faults by the accumulation of the Quaternary tectonic strain. However, surface expressions of the Quaternary tectonic activity had not been reported near the epicenter of the earthquakes before the site construction. Unusual, large-scale water-escaped structures were identified 4 km away from the epicenter during a post-seismic investigation. The water-escaped structures comprise Miocene mudstones injected into overlying Pleistocene coastal sediments that formed during Marine Isotope Stage 5. This indicates the vulnerable state of the mudstones long after deposition, resulted from the combined effects of rapid tectonic uplift (before significant diagenesis) and the development of an aquifer at their unconformable interface of the mudstone. Based on the detailed field analysis and consideration of all possible endogenic triggers, we interpreted the structures to have been formed by elevated pore pressures in the mudstones (thixotropy), triggered by cyclic ground motion during the earthquakes. This interpretation is strengthened by the presence of faults 400 m from the study area, which cut unconsolidated coastal sediment deposited after Marine Isotope Stage 5. Geological context, including high rates of tectonic uplift in SE Korea, paleo-seismological research on Quaternary faults near the study area, and historical records of paleoearthquakes in SE Korea, also support the interpretation. Thus, epicenter and surrounding areas of the 2017 Pohang Earthquake are considered as a paleoseismologically active area, and the causative fault of the 2017 Pohang Earthquakes was expected to be nearly critical state.

• Geotechnical Engineering
• /
• v.9 no.2
• /
• pp.41-54
• /
• 1993

This paper presents the two and three -dimensional stability analysis of nonhom- ogeneous, c-o soil slopes. Potential failure surface is assumed as a logspiral curve refracted in boundaries of layers. In 3-D analysis, rotational soil mass is assumed with a cylindroid central part terminated with plane ends. Seismic force is considered by sesmic intensity. The program developed in this study is compared with the program PCSTABLS. The ratio of three-dimensional minimum factor of safety to two-dimensional case is examined and factor of safety changes are showed for the ratio of cylindroid length to slope height and numbers of slice. On such bases the following conclusions may by made : (1) The program developed in this program is less conservative than the program PCSTABLS. (2) The value of F2 of this study shows the larger differences than that of PCSTABLS with increasing friction angle (3) Factors of safety computed for 3-D geometry differ considerablely from ordinary 2-D factors of safety. Since Fb/F2 exceeds unity, three -dimensional effects tend to increase the factor of safety. (4) As the ratio of three - dimensional failure width of slope height, b/H increase, the value of Fb/Ff decreases and approaches 1.0 when bye is 14. (5) In calculating the factor of safety using the developed program the number of slices is suitable with the ranges of 30-40

• Journal of the Korean Geotechnical Society
• /
• v.29 no.8
• /
• pp.5-14
• /
• 2013

Coarse granular geomaterials containing large gravels are broadly used for construction of large geotechnical systems such as dams, levees, railways and backfills. It is necessary to evaluate deformation characteristics of these materials for dynamic analysis, e.g. seismic design. This study presents evaluation of dynamic deformation characteristics of coarse materials using large scale resonant column testing apparatus, which uses specimens with 200 mm in diameter and 400 mm in height, and the effects of gradation characteristics on maximum shear modulus, shear modulus reduction curve and damping characteristics were investigated. From experimental study using rock-fill materials for a dam, we could see that the largest or mean particle size affects the shape of shear modulus reduction curve. When the specimens are prepared under the same conditions for maximum particle size, the coefficient of uniformity affects the confining stress exponent of maximum shear modulus. It could be concluded that the maximum particle size is an factor which affects shear modulus reduction curve, and that the coefficient of uniformity is for small strain shear modulus, especially for the sensitivity to confining stress.

• Journal of the Korea Concrete Institute
• /
• v.28 no.2
• /
• pp.205-212
• /
• 2016

This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide ($Al_2O_3$) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of $Al_2O_3$ enhanced hydration. The 2M KOH + 16% $Al_2O_3$ and 4M KOH + 16% $Al_2O_3$ specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% $Al_2O_3$ was 46% higher than that of 2M KOH (without $Al_2O_3$). Also, the strength at 28days of 4M KOH + 16% $Al_2O_3$ was 44% higher than that of 4M KOH (without $Al_2O_3$). Increase the $Al_2O_3$ contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of $Al_2O_3$ adversely decreases the water absorption and porosity. Higher addition of $Al_2O_3$ in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with $Al_2O_3$ addition.

• Journal of Korean Society of Steel Construction
• /
• v.22 no.3
• /
• pp.281-291
• /
• 2010

In this study, a five-story steel frame was designed in accordance with KBC2005 to evaluate the effects of the beam-column connection on the structural behavior. The connections were designed as fully rigid and semi-rigid. The fiber model was used to describe the moment-curvature relationship of the steel beam and the column, the power model for the moment-rotation angle of the semi-rigid connection and the three-parameter model for the hysteretic behavior of the steel beam, column, and connection. The structure was idealized as separate 2-D frames and as connected 2-D frames. The peak ground accelerations of four earthquake records were modified in a time-history analysis for the levels of the mean return period and for the maximum base-shear force in a pushover analysis. The top story displacement, base-shear force, story drift, demanded ductility ratio for the semi-rigid connection, maximum bending moment of the column, beam, and connection, and distribution of the plastic hinge were examined in the time-history analysis. The frame with the semi-rigid connection yielded a lower base-shear force, less magnitude, and increasing ratio in the bending moment of the column, beam, and connection than the frame with a fully rigid connection. The TSD connection was deemed to have secured the economy and safety of the sample structure that was subjected to seismic excitation for the Korean design level.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.20 no.6
• /
• pp.523-531
• /
• 2008

In hole type CPTu equipment which combines the concepts of inhole test method and piezocone test method was newly developed in order to evaluate the dynamic properties of marine soils. It is possible to perform inhole type CPTu without any additional source device because the source and receiver are contained inside the cone rod, which is different from the conventional seismic cone system. In this study, laboratory tests using kaolinite as soft soil and numerical simulations using finite element method were carried out to investigate the effects of several parameters including test methods and soil conditions on the test results from inhole type CPTu and to find out the optimum test method. It was found that it is necessary to maintain the length of swing arm as well as the distance between source and receiver consistently to obtain the rigorous test results. The laboratory test and numerical results also reveal that contrary to the input wave frequency, the water content of soil layer and the disturbance due to the installation of swing arm apparently affect the shear wave velocity.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.12
• /
• pp.113-120
• /
• 2008

One-dimensional site response analysis is widely used to simulate the seismic site effects. The equivalent linear analysis, which is the most widely used type of site response analysis, is essentially a linear method. The method applies constant shear modulus and damping throughout the frequency range of the input motion, ignoring the dependence of the soil response on the loading frequency. A new type of equivalent linear analysis method that can simulate the frequency dependence of the soil behavior via frequency-strain curve was developed. Various forms of frequency-strain curves were proposed, and all curves were asserted to increase the accuracy of the solution. However, its validity has not been extensively proven and the effect of the shape of the frequency-strain curve is not known. This paper used two previously proposed frequency-strain curves and three additional curves developed in this study to evaluate the accuracy of the frequency-dependent equivalent linear method and the influence of the shape of the frequency-strain curves. In the evaluation, six recordings from three case histories were used. The results of the case study indicated that the shape of the frequency-strain curve has a dominant influence on the calculated response, and that the frequency dependent analysis can enhance the accuracy of the solution. However, a curve that results in the best match for all case histories did not exist and the optimum curve varied for each case. Since the optimum frequency-strain curve can not be defined, it is recommended that a suite of curves be used in the analysis.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.3
• /
• pp.155-163
• /
• 2023

Real-time monitoring technology is critical for ensuring the safety and reliability of nuclear power plant structures. However, the current seismic monitoring system has limited system identification capabilities such as modal parameter estimation. To obtain global behavior data and dynamic characteristics, multiple sensors must be optimally placed. Although several studies on optimal sensor placement have been conducted, they have primarily focused on civil and mechanical structures. Nuclear power plant structures require robust signals, even at low signal-to-noise ratios, and the robustness of each mode must be assessed separately. This is because the mode contributions of nuclear power plant containment buildings are concentrated in low-order modes. Therefore, this study proposes an optimal sensor placement methodology that can evaluate robustness against noise and the effects of each mode. Indicators, such as auto modal assurance criterion (MAC), cross MAC, and mode shape distribution by node were analyzed, and the suitability of the methodology was verified through numerical analysis.